The role that hydrogen and sulfur play in desktop failure of thermal barrier coatings, Part 2

During normal service conditions the thermal barrier coatings fail (i.e. top coat spalation) typically during cooling from high temperature. A type of delayed top coat spalation, namely "desk top failure", has become of both theoretical and technical interest. This delayed failure mode is the observed top coat spalling several days after the sample is removed from the high temperature environment and is cooled to room temperature. H₂O in the environment and sulfur, be it from the environment or be it sulfur contained in the bond coat of substrate alloy, are supposed to have a strong influence on top coat adhesion, spallation and life time of the TBC system. Because desk top spallation occurs in ambient air the working hypothesis is that the humidity from the office environment plays a role in desk top failure.